The present invention relates to an apparatus for producing a tube with successive corrugations of different configuration and especially of different radial extension from a tubular blank of constant diameter.
The DE-AS No. 13 03 671 discloses an apparatus for continuous production of annular corrugations of substantially equal configuration from a tubular blank of constant diameter. This apparatus comprises a stationarily mounted vertically arranged core pin which is provided with an axially extending hollow section for guiding a multiple part tube mandrel as well as a piston-like enlargement at the free end of the shaft section, which forms an abutment for radially movable, hydraulically operated holding and forming jaws. After pushing a smooth-walled tubular blank onto the core pin, the holding and forming jaws are first moved in engagement with the blank to press the latter against the piston-like enlargement. Subsequently thereto, clamping jaws are pressed by means of radially arranged hydraulically operated cylinder-and-piston units connected with the mandrel against the blank, whereby the mandrel supports the blank inwardly at the region of the clamping jaws. Between the piston-like enlargement, the tubular mandrel and the tubular blank there is now formed an annular expansion space which is impinged by pressure fluid fed into the space through the hollow shaft and a crossbore, so that the wall of the tubular blank bulges outwardly. After the bulge reaches a predetermined dimension, the tubular mandrel together with the clamping jaws and the clamped blank is moved by means of hydraulically operated cylinder-and-piston units arranged parallel to the core pin in direction toward the piston-like enlargement, whereby the tubular wall is expanded and an annular corrugation is formed.
A disadvantage of this known apparatus is the necessary sealing of the expansion space in the region of the piston-like enlargement and that of the tubular mandrel. Sealing rings of elastic material are provided for this purpose, which are axially compressed to thus be radially deformed and pressed against the inner surface of the tubular blank, respectively against the previously produced corrugation. The compression of the seal in the region of the piston-like enlargement and that of the tubular mandrel is produced by cylinder-and-piston systems which are axially displaced by hydraulic fluid. The elastic seals are, during forming of corrugations in the blank, continuously compressed and again released, so that the material will necessarily fatigue, respectively be worn, which will result in leakage, and in addition the cylinder-and-piston units for the compression of the elastic seals have to be properly sealed.
The therewith-connected necessary exact fits and seals considerably increase the manufacturing cost. In addition, increased maintenance cost is necessary in order to assure a proper function of this apparatus. Especially disadvantageous in this known construction is the necessary feeding of the hydraulic fluid to the cylinder-and-piston unit in the multipart tube mandrel. For this purpose, there is provided in the hollow shaft an additional tube. It is also of disadvantage that the cylinder-and-piston unit in the piston-like enlargement is to be supplied with hydraulic pressure fluid. For this purpose an additional conduit is provided at the outer end of the piston-like enlargement. This necessary additional tube will complicate the removal of a finished corrugated tube, as well as the placement of a new tubular blank into the apparatus. An automatic feeding of the blanks is, therefore, impossible. In addition, the known apparatus needs, due to its construction, a large installation space.
Another apparatus for continuous production of successive corrugations of substantially uniform configuration is disclosed in the application Ser. No. 40,275, filed May 18, 1979, now U.S. Pat. No. 4,237,713.
The object of this last-mentioned apparatus is to provide an apparatus of the aforementioned kind which is compacter than such apparatus known in the art, which will operate substantially trouble-free, and which facilitates automatic feeding of the tubular blanks into the apparatus and removal of the finished corrugated tube therefrom. This known apparatus mainly comprises support means, a central pin having an elongated shaft portion fixedly attached only at one end to the support means and having a radially enlarged head portion at the other end, a tubular member mounted on the shaft portion of the central pin for movement in axial direction and adapted to support together with the head portion in a tubular blank at the inner surface therefrom, in which the tubular member has one end axially spaced from the head portion to form between this one end and the head portion and a blank supported thereon an expansion chamber. The apparatus includes further first clamping means comprising a plurality of hydraulically operated radially movable holding and forming jaws opposite the head portion, second clamping means comprising a plurality of circumferentially displaced radially tiltable clamping fingers of a collet arranged in the region of the one end of the tubular member about the outer circumference of the blank supported by the latter, a hydraulically operated axially movable annular clamping piston surrounding the clamping fingers for moving the latter between a clamping and a releasing position, an upsetting cylinder connected at one end to the other end of the tubular member and having opposite this one end a radially enlarged end portion surrounding and guiding the clamping piston for movement in axial direction. This known apparatus further includes an axially movable corrugation cylinder surrounding part of the upsetting cylinder and being formed with an annular groove, an annular collar fixed to the upsetting cylinder and located in the aforementioned annular groove of the corrugation cylinder and forming in this groove two chambers adapted to be alternatingly filled with pressure fluid so as to axially move the upsetting cylinder relative to the corrugation cylinder, and means for feeding pressure fluid into the aforementioned expansion chamber after axially spaced portions of the blank have been clamped against the head portion and said one end of the tubular member by the first and second clamping means to thus expand a portion of the blank clamped between the first and the second clamping means into a corrugation.
This will provide a construction which, compared with the construction of the other above-discussed prior-art apparatus, has only a small radial extension beyond the outer circumference of the tubular blank. Thus the apparatus can be installed in a relatively small space. Furthermore, the means for clamping the tubular blank and to advance the latter to form the corrugations are arranged closely about the tubular blank. No cylinder-and-piston units, which require closely fitted parts and seals liable to wear are provided in the interior of the tubular blank. The tubular member mounted on the shaft portion of the pin is an integral part guided along its total length on the shaft portion.
An additional advantage of the construction of the last-mentioned apparatus is that the central pin is mounted only at one end thereof on the support means, whereas on the other end no tube for feeding hydraulic fluid is necessary. This provides free access to the apparatus so that an automatic feeding of the tubular blanks into the apparatus and removal of the finished corrugated tube are possible. The gripping of the tubular blank occurs by means of axially directed clamping fingers, which by means of a clamping piston, movable relative to the clamping fingers, are pressed against the tubular blank, so that the latter in turn is pressed against the members extending therethrough. Due to the projection of the annular collars into the corresponding annular grooves, circumferentially extending pressure chambers are formed so that by feeding pressure fluid into the latter, a predetermined displacement of the various parts in the desired direction is accomplished. The expansion space between the head portion of the central pin and the tube mandrel is sealed by simple metallic seals on the clamping and forming jaws and the clamping fingers. Additional extensive sealing systems as are necessary in the known apparatus, are avoided.
A corrugation is formed by axially displacing the upsetting cylinder relative to the corrugation cylinder, while the tubular blank is clamped and the relative movement of the two cylinders establishes the axial dimension of the corrugation.
The central pin is relatively simple in its construction since it has only a longitudinal bore and a crossbore through which the pressure fluid is fed into the expansion space.
According to an advantageous feature of the last-mentioned apparatus, the corrugation cylinder is provided with a second annular groove, axially spaced from the first-mentioned annular groove, and the arrangement includes a sleeve fixedly connected to the support means and having an inner surface guiding the upsetting cylinder and an outer surface guiding the corrugation cylinder. The sleeve has an annular collar projecting into the second annular groove of the corrugation cylinder and dividing the annular groove into two compartments adapted to be alternatingly filled with pressure fluid so as to axially move the corrugation cylinder in one and the opposite direction relative to the sleeve.
According to a further feature of the last-mentioned apparatus, a pair of adjusting nuts are axially adjustable connected to opposite ends of the corrugation cylinder, whereby the adjusting nut in the region of the radially enlarged end portion of the corrugation cylinder serves to adjust the compression stroke, whereas the other adjusting nut serves to steplessly adjust the distance between successive corrugations.
Even though the aforedescribed construction permits to change the compression stroke, as well as the distance of successive corrugations to change in dependence of the respective desired dimensions of the corrugations, the sequence of operations will be fixed for any adjustment carried out on the apparatus. The radial dimensions of the corrugations and the distance between successive corrugations will thus remain the same over the total length of the corrugated tube. In this known construction an inadmissable high manual expenditure would be necessary to produce a corrugated tube which over its length has stepless, or in successive steps, different radial dimensions, respectively different axial distances between successive corrugations.